The world’s top discussion moderators have developed successful tools for keeping online miscreants from disrupting conversation. All are rooted in one psychological insight: If you simply ban trolls — kicking them off your board — you nurture their curdled sense of being an oppressed truth-speaker. Instead, the moderators rely on making the comments less prominent.

Patient Zero here is Slashdot, the tech site that pioneered one elegant way to police trolls: crowdsourcing. Slashdot has an automated system that randomly picks a handful of readers and gives them, for a day or so, the power to describe others’ comments with terms like “funny” or “off topic.” Those descriptions are translated into a score from -1 to 5. Readers can set their filters so they see only comments with high ratings — and trollery effectively vanishes. One academic study found that the majority of Slashdot readers filter out comments rated 2 or lower. Indeed, the concept of crowd-voting has worked so well that sites as high-traffic as the The New York Times now use it.

Here’s another hack: selective invisibility. It was invented by Disqus, a company whose discussion software handles the threads at 90,000 blogs worldwide (including mine). In this paradigm, if a comment gets a lot of negative ratings, it goes invisible. No one can see it — except, crucially, the person who posted it. “So the troll just thinks that everyone has learned to ignore him, and he gets discouraged and goes away,” chuckles Disqus cofounder Daniel Ha.

My personal favorite innovation is disemvoweling, a technique pioneered by Teresa Nielsen Hayden, who moderates the discussion threads at the geek-culture blog Boing Boing. Whenever Nielsen Hayden encounters a nasty post — an ad hominem attack, for example — she leaves it up but removes all the vowels: y r fckng sshl, for example. The result is incoherent enough that it’s neutered, yet coherent enough that no one can cry censorship. The comment hasn’t vanished.

Best of all, because disemvoweling is visible, it trains the community. “You’re teaching the other commenters what the lines are by showing them comments that have stepped over the line,” Nielsen Hayden says.

Now, most veteran moderators will tell you that automated systems and crowdsourcing go only so far. Most told me that if you’ve got a high-volume site with political content — like Whitehouse.gov — you’ll also need to moderate postings by hand, hiring staff to look over each comment and delete the truly crazy hate-speech ones. The Huffington Post employs up to 25 people at a time to comb through its 35,000 comments a day.

If the White House were to use humans to filter posts, it could get into some dicey political situations. If it were to outright ban them, it could draw First Amendment lawsuits. So the genius of modern troll-taming techniques — leaving trollery intact, but mitigating its impact — neatly fits the bill. Moderation software could grow even more sophisticated at the task, perhaps incorporating collaborative filtering tools that recommend the best posts based on your likes and dislikes.

Mr. President, bring on the trolls. The commentosphere is ready for them.

(The picture above is courtesy the CC-licensed Flickr stream of Robert of Fairfax!)